The present invention relates to propellants and more specifically to solids loaded, extrudable, solventless, doublebase propellants.
Solid propellants are generally classified as being either homogeneous or composite. The former refers to those types, usually containing nitrocellulose, which are considered true monopropellants, each molecule containing all the necessary fuel and oxygen for combustion. The composite type propellant, in contrast, consists of a physical mixture of a fuel and an oxidizer.
The homogeneous nitrocellulose propellants are further subclassified as being either single, or double base, depending on whether the composition contains nitrocellulose as the sole combustible or contains additional nitroxy compounds, such as nitroglycerin, as a second combustible. Additionally, additives or fillers such as plasticizers, represented by phthalates and and triacetin; stablizers, represented by 2-nitrodiphenylamine, tertiary butylcatechol and ethyl centralite; burning rate modifiers, such as lead salts; extrusion lubricants, represented by stearates, soaps and waxes; and flash suppressors, such as potassium salts are incorporated into the propellant to help meet different ballistic requirements.
More recently, small percentages of additional oxidizers such as ammonium perchlorate and HMX have been added to the standard double-base propellant. These new propellants are termed either solids loaded double-base or composite-modified double-base propellants.
There are at least two methods presently available for producing these types of propellants; the "solvent" and the "solventless" techniques. In the "solvent" process, solvents such as acetone or ether-alcohol mixtures are used to dissolve and colloid nitrocellulose to form a viscous or doughy mass. The mass is granulated, usually by extrusion, and the volatile solvent is recovered as completely as possible. Although the "solvent" process produces a product of fair mechanical strength, difficulties are encountered in obtaining good ballistic properties. The "solventless" process avoids these limitations by eliminating entirely the need for volatile solvents to colloid the nitrocellulose. According to this process, nitrocellulose is slurried in a nonsolvent to form a paste-like mixture which is dried and rolled on hot rolls. The resulting colloided sheet is extruded or cut into the desired granulation. Although the product produced by the "solventless" process is generally characterized by good ballistic properties, it is nevertheless generally inadequate for those missile systems requiring a greater degree of mechanical strength. Previous attempts at strengthening "solventless" propellants have proved generally ineffective since they have concentrated on variations of ingredients and proportions which resulted in serious changes in ballistic parameters and workability.